Heat sinks are used in a variety of electronic devices to dissipate heat from the device, preventing any failure of or damage to the device. Heat sinks are made of a variety of heat conducting materials and are formed in a variety of shapes to adequately conduct the heat from the device. One application of a heat sink is a lid used with an integrated circuit to reduce the heat of the semiconductor die to enable the integrated circuit to function properly. One purpose of the lid is to keep a semiconductor junction, such as a junction of the transistor, below a maximum specified operating temperature.
Typically, flip chip packages are thermally enhanced ball grid arrays (BGAs) with die facing down. They are provided with an exposed metal heat sink at the top. These are considered high-end thermal packages and lend themselves to the application of external heat sinks, either passive or active, for further heat removal efficiency. However, these types of conductive lid heat sinks often exhibit the problem of separating from the top of an integrated circuit package. Because the adhesion strength of the adhesive is sometimes not strong enough to hold the conductive lid to the package, the conductive lid can come off of the package.
A lid for an integrated circuit, commonly made of a metallic or ceramic material, is attached on top of a flip chip package to provide protection to the silicon die and other discrete surface mount components and to increase thermal conductivity of the package. Proper material construction and processing of the lid, the package, and the adhesive is required so that the lid will stay attached to the package during the assembly and long term field usage. Degradation of the adhesive can be caused by many factors, including improper dispensing of adhesive that does not produce full adhesive surface as designed, shear stresses introduced by thermal expansion/shrinkage differences at the interfaces, push/pull stresses introduced by silicon/package/board warpage, adhesive degradation due to chemical attack, etc. Excessive component handling stresses during test, assembly, or rework, such as excessive torque or pressure, can also result in separation of the lid from the package.
Accordingly, there is a need for an improved lid for an integrated circuit and method of securing a lid to an integrated circuit.